The control of microorganisms such as bacteria, mold, mildew and algae in humid environments or on moist surfaces has long been a matter of concern. Biocidal compositions containing phenols, iodine, or quaternary ammonium compounds and heavy metals such as tin and mercury have been used, but these suffer from the drawback of lacking permanence and must be reapplied periodically to maintain protection. In addition, many of these compounds are toxic to higher forms of life. Polymeric coatings entrapping a biocide which is slowly released upon wetting the coated surface are described in the patent literature by Oakes et al., U.S. Pat. No. 5,061,485 and Patel et al., U.S. Pat. No. 5,585,407. The coatings are generally acrylate copolymers that have functional groups to improve the quality of the coating or facilitate its removal. Although the duration of protection is extended, the biocide is leached from these coatings and the coating must be renewed periodically to maintain its biocidal properties. Further, if coatings with releasable antimicrobial compounds are used on outdoor surfaces such as roofing felts or lumber, the antimicrobial substance may be released to the environment with potential adverse effects to desirable flora and fauna.
Various attempts have been made to overcome these deficiencies by chemically bonding the active antimicrobial substance to the polymeric coating. Polysiloxane polymers having pendant quaternary ammonium salts are disclosed by Nohr, et al., U.S. Pat. No. 5,569,732 and Gettings et al., U.S. Pat. No. 5,013,459. The polymers disclosed in these patents have been applied to fibers, non-woven fabrics and glass or ceramic surfaces. Polymers and copolymers from vinyl benzene having quaternary ammonium salt groups have been disclosed by Sheldon et al., U.S. Pat. No. 4,532,128 for use with various medical and personal care products.
Polyurethane coatings having biocidal properties were reported by Nurdin, et al., Journal of Applied Polymer Science, vol. 50, 651 (1993). The polyurethanes were made from dihydroxytelechelic polybutadienes to which quaternary ammonium tetramethyldisiloxanes had been grafted before forming the urethane polymer. The Nurdin et al. polyurethanes are highly functional and form crosslinked, thermoset materials. Similarly, Wang and Lin, Journal of Polymer Research, vol. 5, 177 (1998), reported antimicrobial fabric finishes made from polyurethanes to which quaternary ammonium siloxanes had been attached through epichlorohydrin grafted to the polymer chain. Wang and Lin use dimethylformamide to form solutions for applying their polyurethanes to a substrate. In these references rather complex and relatively expensive chemistries are used to attach quaternary ammonium groups to a polyurethane polymer.
Polymerizable compositions having acrylate monomers with pendant quaternary ammonium groups are described by Imazato et al., U.S. Pat. Nos. 5,408,022 and 5,494,987. The Imazato compositions provide an unreleasable antimicrobial polymer useful for applying to the surface of medical articles, in general, and as a restorative material for dental caries, in particular. Various crosslinkable copolymer compositions are described. A polyurethane having an acrylate group at each of its molecular ends is used as a difunctional crosslinking agent for the acrylate polymers and allows properties of the acrylate polymers, such as, hardness, strength and thermal resistance of the antimicrobial polymer to be varied according to the requirements of the intended use. These materials are completely endcapped. Based on the disclosed chemistry, these compositions do not form an aqueous dispersion and when applied as a coating are cured or polymerized on the surface.
Biocidally active coating compositions having pendant quaternary ammonium groups are described by Stovicek, U.S. Pat. No. 5,084,096 for treating surfaces submerged in sea water, construction materials intended for outdoor use, environmental surfaces in health care facilities and for treating the ducts of HVAC systems. Coating compositions are disclosed which incorporate repeating units of a diol monomer having an alkyl or arylalkyl quaternary ammonium group directly bonded by an alkylene group to the backbone of polyester, polyether, and polyurethane polymers. The diol monomers have limited utility with respect to polymer formation which in turn limits the ability to vary the properties of polymer coatings.
The polymers of the present invention are relatively easy to make in a pure form with a low level of residual, extractable material, and preferably with no residual, extractable material. The prior art fails to teach polyurethane coating compositions having immobilized or bound biocidal quaternary groups and that have the added capability to vary the polymer structure to adapt the properties of the coating to particular uses. In addition, the prior art fails to teach film forming polyurethane polymers having covalently bound polymer groups derived from polymerization of vinylic monomers which at least in part comprise biocidal quaternary ammonium groups. Further, the prior art does not teach polyurethane coating compositions having bound biocidal quaternary ammonium groups that can form aqueous dispersions or solutions thus eliminating the need to use potentially flammable and toxic solvents.